limiting FTP access to a subdirectory

[steam]

Hello.

I must forbid the FTP access to a subdirectory, in a customer virtual host.
I cannot work with chown since the server is running cgis under suexec. So I cannot change the user owning the cgi files.

In short, I'm looking for a method to manage the subdirectory via ftp (i.e. path/to/USER/

http://www/subdir)

with ANOTHERUSER. So USER will not read 'subdir'.

Any suggestions?

Thank you.